The present invention relates generally to the field of electrical machines, such as electric motors. More particularly, the invention relates to a technique for insulating windings or coils in such machines to improve their construction, performance and useful life.
A wide range of applications exist for electric motors, generators, and similar rotating electrical machines. In a vast array of industrial, consumer and other applications, for example, electric motors are used as a prime mover for pumps, material handling equipment, process equipment, drives, and so forth, to mention just a few. In general, such machines include a housing in which a stator is statically positioned. A rotor is dynamically mounted within the stator and is inductively driven in rotation by an oscillating electric power source applied to coils or windings of the stator. The stator windings are typically disposed within radial slots to create controllable magnetic fields which are forced to rotate by appropriate application of power to the windings during operation. An output shaft coupled to the rotor serves as an interface for driving other equipment in the particular application.
One challenge in designing and assembling electrical machines such as electric motors is in the specific design and assembly of the machine""s magnetic coil windings. Stator windings specifically, may be formed as a series of turns of electrically conductive wire, or of a single-piece bar. In either case, leads extending from an end of the coil winding serve to accept electrical power applied to the coils during operation. However, the coil must generally be electrically isolated (i.e. insulated) from the stator core in which it is installed, as well as from other electrically conductive portions of the machine and housing, and from other coils installed within the machine.
To provide insulation at such locations, prior art techniques included winding of insulative tapes around the magnet wire, coil or portions of the coil. In a typical process, for example, a region between end leads of the coil is covered with a series of progressive wraps of an insulating tape. The insulating tape is then cut and secured following wrapping around the coil end region. The leads may then be bent back into place over the end region, and the taping process is restarted around a main body portion of the coil. The insulating tape is then cut and re-secured after taping this portion of the coil. These operations may be performed by hand, or in a specially designed machine. Typically, some of the operations are performed in the machine, while operator intervention may be required during certain steps in the process. When the operation is completed by hand, a continuous insulation of the lead may be obtained. However, hand taping the coil compromises dielectric properties and severely limits manufacturing throughput.
Current techniques for tape insulation of machine coils of the type described above suffer from a number of drawbacks. For example, the process may result in excessive layering of insulation material at a point where the lead exits the coil. In accordance with the present technique, it is believed that this is caused or aggravated by cutting the insulating tape between the process for insulating the end region and that for insulating the main body portion of the coil. The process also can result in loss of time in severing the insulating tape, positioning the tape for covering the main body portion of the coil, and restarting the wrapping process for the main body portion. The lead seal junction may also be somewhat compromised, sometimes resulting in less than optimal dielectric properties in the area where the tape wraps are stopped and restarted around the coil leads. Such reduced dielectric strength can, in turn, result in a shortened life of the coil, the stator and the overall machine in which these are installed.
Therefore, there is a need for an improved technique for insulating windings, coils and similar structures in electric machines. There is a particular need, at present, for a technique which facilitates continuous machine insulation of coils, while avoiding the drawbacks of existing techniques, particularly in insulating of locations where leads exit a main coil body.
The present invention provides an improved technique for insulating machine coils designed to respond to such needs. The technique may be applied in a wide range of settings, but is particularly well-suited for machine insulation of electric motor coils through the use of multiple layers of insulating tape. The tape may be applied from one or more sources, typically tape spools or similar repositories. The coil leads are displaced from the end region of the coil and insulating tape is wrapped around this section of the coil body. The coil leads may then be attached back to the insulated end region, and winding of tape over a main region of the coil continued without severing or interrupting the insulating tape. Regions of the coil may be covered with a plurality of wraps of insulating tape, particularly at regions where additional dielectric strength is desired, or where friction or wear may take place. Moreover, a pitch of tape wraps may be varied at one or more locations along the end region adjacent to the leads, or elsewhere on the main region of the coil. An armor tape may be applied over all or a portion of the insulating tape to finish the insulating tape application process.
The inventive technique offers distinct advantages over existing techniques. For example, the technique offers optimized dielectric properties in regions adjacent to the location where coil leads separate from the main region and end region of the coil. The technique also offers a rapid and cost-effective solution for improved insulation of coils in machine taping applications. The technique is more efficient and cost effective than existing techniques in which tapes are severed or cut and reapplied to a main body region of a coil. Following insulation of the coil in accordance with the present techniques, the coil may be processed and installed in a machine, such as an electric motor, in any one of a variety of configurations, such as to form single-phase or three-phase electric motors, generators, dynamos, and so forth.